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Correction: We've since been informed that the team plans on using a luciferin/luciferase system from bacteria, which operates through a completely unrelated mechanism to the one used by fireflies. In this case, six enzymes are involved in converting a fatty acid to a substrate for the light-generating reaction. This should allow the entire system to work in plants without the need for any external supply of chemicals.

This makes the challenges of getting the firefly system to work in plants irrelevant to this project. The energetic challenges of producing sufficient light without killing the plant, however, remain significant.

Could we eventually do away with streetlights and have our neighborhoods bathed in the diffuse glow of self-lit trees? That's the premise behind a new Kickstarter campaign that has been featured on TXNOLOGIST and Slashdot. As of this writing, the project has already received more than double its goal of $65,000, with each donor being promised a glowing plant. Long-term, the project's leaders hope to expand out to trees, which is why their promotional video talks about doing away with streetlights.

There's just one small problem: as planned, the plants won't glow. At least not without a fertilizer that costs $200 a gram. Even if the team were to overcome this hitch, trees would probably never generate enough light to do away with a street lamp.

If you follow the biosciences, you'd be forgiven for thinking that glowing creatures were a dime a dozen. For example, researchers are regularly creating glow-in-the-dark mice and fish, and the technique has been used in a variety of species. But all of this work relies on the green fluorescent protein (GFP) and its relatives, which glow in other colors. GFP is great, and it's truly worthy of the Nobel Prize in Chemistry that its development was awarded. But bioluminescent animals only glow in the sense that black light posters do: they require UV light to excite the molecule, which then releases energy in the visible spectrum.

A GFP tree would glow during the day (when it wouldn't be noticed), then it would quickly fade as the sun sets. No streetlight there.

The complicated glow of fireflies

The people behind the new tree realize that limitation, so they've gone with a different form of glow—the one that powers fireflies. The protein that allows fireflies to glow, called luciferase, works in a completely different way from GFP. Rather than taking energy from light and re-emitting it, it converts chemical energy to visible light. Some of that energy comes from ATP, the chemical that all cells use to drive their energy-hungry chemistry, plants included. So that part is not a problem.

The other part of the energy involved in the glow comes from a complex molecule called a luciferin, shown below. And that's where problems arise.

As far as I can tell, we have no idea how fireflies make this chemical. Part of the synthesis reactions involve an amino acid (cysteine) that plants would be expected to have. But that cysteine has to react with chemicals of unknown origin to make the structure above. A recent text, Biosynthesis in Insects nicely describes just how mysterious the creation of luciferin is:

Astonishingly, the biosynthetic pathway for the formation of luciferin is unknown. Indeed, it is not even clear to which family of metabolites it is related. Luciferin is said to be synthesized by the fusion of benzoquinone (of unknown origin), cysteine, and a nitrogen source to give 2-cyano-6-hydroxybenzthiazole, but this has not been proved. The benzthiazole is said to condense with a second molecule of cysteine before oxydation and rearrangement in an unexplained way...

Plants simply don't make the stuff. Because we don't know how fireflies make it, we can't just take their genes and put them into plants. We know the luciferase system works in plants, but it only works because we add luciferins to their growth medium, and luciferins are currently running at about $200 a gram.

The people behind the project aren't completely ignoring this issue. One of the genes they're planning on putting into the plants is a recycling enzyme that takes the products of the light-producing reaction and recombines them into luciferins. But without any luciferins to begin with—as well as a constant supply, since the recycling won't be 100 percent efficient and the plant will grow new leaves—there would be nothing for the recycling enzyme to work with.

In short, the plants they're going to be sending out to their backers won't actually glow. Getting them to do so will require fertilizing them with luciferins, which are quite pricey.

A matter of energy

At some point in the future, we might be able to figure out how fireflies make this molecule, and we could put all of the requisite genes into a plant. Would we be ready to do away with streetlights then? Probably not, and not just because most trees go into an energetic stasis during winter.

Streetlights come in a variety of intensities, but a ballpark figure seems to be about 10,000 lumens. The trees would have the incident sunlight to work with as the source of energy for their glow, and that dwarfs the streetlight, at 100,000 lumens per square meter. Of course, plants can't use most of that energy for a number of reasons: it's the wrong wavelength, it gets reflected, it misses their leaves, etc. Photosynthesis isn't 100 percent efficient, either. By the time all of these factors are accounted for, the typical plant captures somewhere between three and six percent of the incident sunlight. Going with five percent, we're now down to 5,000 lumens

Of course, that's for every square meter, and each streetlight illuminates a lot of square meters. At the same time, the tree won't be able to use all of its energy to make light or it would promptly die. Plants seem to have some energy to spare—they carry around a lot of superfluous DNA and grow excessively ornate flowers—but there are limits to how much energy they can spare and still keep growing. For argument's sake, let's say they can spare about five percent of their total energy for producing light. That takes us down to 250 lumens for each square meter of foliage, or about the equivalent of a 40W bulb.

But most of that energy will never get made into light. Remember, even basic chemicals like cysteine don't come for free; they cost energy. So does making the enzymes that convert them into more complicated chemicals, as well as (typically) the reactions they catalyze. Then you have to make the luciferase enzyme, as well as the recycling enzyme, and power those. Absolutely none of these processes are going to be 100 percent efficient.

You'd be extremely lucky if five percent of the energy being dedicated to producing light ever ends up getting used that way. We're now at 12.5 lumens.

Of course, about half that light would be pointed directly at the sky, and it wouldn't do much good as far as illumination goes. A lot of what's emitted downward will end up being directed back at the tree's branches and trunk, which will absorb some of it. Some other fraction will be absorbed by the cells in which it's emitted (some of it probably by the chlorophyll that powered the process in the first place). That leaves us with under 5 lumens of potential light for every square meter of foliage, and likely much less.

All of which places this on the very edge of being useful directly under a tree. If any of the above estimates turn out to be wrong—or you get too far from the tree—then all bets are off. Streetlights probably have a long career ahead of them.

The project won't work as things stand, and it probably won't even do what's being promised in the future. If those were the only problems with this project, they would be significant ones. But the fact is that the project is largely recreating the wheel; various academic labs already have luciferase working in plants, including in the arabidopsis species that the project plans on sending out to its backers. Even if you wanted to start from scratch, there are cheaper ways of going about making the DNA required than ordering up the DNA online, one base at a time. Plenty of researchers would send the DNA for the luciferase for free.

All of which would leave me extremely skeptical of this project. I don't doubt that the project leaders will spend the money they get as they promise to; I just doubt that the money is going to be spent efficiently (or to any useful end).

The people behind this project have not yet responded to a request for comment.